During one phase of producing steel, up to 400 tons of molten steel at a temperature as high as 3000.degree. F., is contained in a vessel below a layer of slag, of approximately 2000.degree. F. Typically the steel is dispensed through a hole in the bottom of the vessel into a tundish, from which the steel is then dispensed into caster molds. A conventional slide gate is often utilized to control the flow of molten steel/slag from the vessel.
To maintain high quality steel as an end product, it is desired that none of the slag exits the vessel into the tundish, thereby contaminating the end product. Various methods have been utilized in an attempt to accomplish this. One way is simply to overestimate the amount of slag, and to close the slide gate while there is still a buffer layer of molten steel in the vessel, to prevent slag from exiting into the tundish. However, this results in many tons of wasted steel per batch, as the steel remaining in the vessel will either result in scrap, or be utilized as a lesser grade steel product.
Alternatively, systems have been provided designed to detect slag exiting through the vessel hole. One system magnetically detects flow of slag through the vessel hole to close the slide gate. However this system is relatively complicated, and only detects slag after it has begun flowing through the vessel hole, thus possibly resulting in a certain amount of slag entering the tundish before complete closure of the slide gate. Similarly, another system disclosed in Netherlands patent 8006347 senses differences in sound pressure to determine when slag is exiting the vessel hole.
In order to better control the flow of the molten slag, it has been found desirable to more precisely know the level of the interface between the molten steel and the slag. Various systems have been proposed for this, such as disclosed in U.S. Pat. Nos., 4,544,140; 4,413,810; 3,610,601; 3,850,416; 5,105,874; 4,880212; and 4,899,994. However, these systems are relatively complex.
The present invention is provided to solve these and other problems.